Abstract
The co-condensation process of high temperature metallic vapors was examined in order to investigate the possibility of synthesizing ultrafine alloy particles from a vapor state. Experimental investigations were made for Nb-Al and Nb-Si systems by using an rf plasma evaporation method. Two kinds of metallic vapors in a plasma flame were quenched and deposited on a water-cooled copper surface. X-ray diffraction analysis of the prepared particles revealed the formation of some compounds, such as NbAl3 for Nb-Al system, and Nb5Si3 for Nb-Si system. Several theoretical investigations were also made for a better understanding of the process. One is about the quenching rate of the metallic vapors, which was estimated by the calculation of the flow patterns and temperature distributions in a quenching region. The second is about the nucleation temperatures of Nb, Al, and Si according to the Lothe-Pound theory. The third is about the particle growth history of Nb. The results showed that the quenching rate was 104–105 K/s and the nucleation temperatures were about 3000 K, 1500 K, and 2000 K for Nb, Al, and Si, respectively.
On the basis of the results of the experimental and theoretical investigations, the co-condensation process of high temperature metallic vapors was discussed. It was found that even if one component was condensed preferentially, composition-controlled alloy particles could be synthesized, provided that the other component began to condense while the former component particles were in a liquid state.
